This invention relates to adding potassium chloride to a refinery process stream of brine containing potassium chloride, sodium chloride and a minor amount of salt impurities to increase and maintain a high concentration of potassium chloride. More therein particularly this invention relates to adding potassium chloride crystals that are precipitated from a pond which is concentrated by solar evaporation and/or cooled by ambient air temperature, or crystals produced from low temperature crystallization, e.g., refrigerated crystallizers or the like, to a potassium chloride refinery process stream.
Potassium chloride is solution mined by causing a solvent to be circulated through a subterranean ore deposit thereof and withdrawing a solution enriched in potassium chloride and sodium chloride. Several subterranean cavities are usually simultaneously developed and each mined upwardly through stratifications having rich and lean potassium chloride content. The combined withdrawn solution, usually saturated with sodium chloride, is processed in a refinery for the production of potassium chloride.
The refinery is designed so that an average concentration of brine from the several cavities can be processed in accordance with the average potassium chloride in the deposit as a whole. But, these designs are usually too inflexible to handle a wide variation of salt concentration in the feed, such as when rich or lean stratifications are mined simultaneously. Consequently, when the concentration of the feed is low, an excess amount of energy is expended per unit of potassium chloride produced and, when the concentration of the feed is high, only an overdesigned system is able to handle the feed.
One method that helps to alleviate the aforesaid problem is a refinery process that includes the use of multiple effect evaporators to concentrate the feed solution with respect to potassium chloride while precipitating sodium chloride. In this method the solution that passes through the first evaporator effect is allowed to become saturated with respect to both potassium chloride and sodium chloride, thereby precipitating both salts and the precipitated salts are forwarded to a hotter effect wherein the potassium chloride is re-dissolved, for example, see U.S. Pat. No. 3,704,101.
In another method, solution mined brine of potassium chloride ore is forwarded to a pond wherein it is concentrated by solar evaporation, thereby precipitating in a slow process both potassium chloride and sodium chloride. The salts are then harvested by machinery which scrapes up all solids including sodium chloride and impurities. Potassium chloride is separated from the sodium chloride and other impurities by froth flotation, which typically yields potassium chloride crystals that are relatively impure and as a consequence must be further purified with respect to sodium chloride content to attain high grade crystals.